Method for associating a PBX extension with a user account of a cloud service application

ABSTRACT

A method for associating a PBX extension ( 21 ) with a user account ( 31 ), the method comprising: (S 1 ) receiving an association request comprising a PBX extension telephone number from a user account ( 31 ), (S 2 ) sending an association code to the user account ( 31 ), (S 6 ) sending to the PBX central unit ( 22 ), a command to connect the PBX extension ( 21 ) to the IVR application ( 33 ), (S 8 ) receiving through the IVR application ( 33 ), an association code from the PBX extension ( 21 ), (S 10 ) if the association code received from the PBX extension ( 21 ) is the same as the association code sent to the user account ( 31 ) enabling the control of the PBX extension ( 21 ) from the user account ( 31 ) through the CTI link ( 51 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to European Patent ApplicationNo. 17305348.9, filed Mar. 27, 2017, entitled “Method for associating aPBX extension with a user account of a cloud service application”, whichis incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to cloud service applications for controlling PBXextensions. A PBX (Private Branch Exchange) is a system that connectstelephone extensions to the Public Switched Telephone Network andprovides internal communication.

BACKGROUND

In the context of an hybrid cloud solution coupling communicationdevices of a PBX system (also called PBX phones or extensions) deployedon customer premises, and a cloud services enabling PBX users to drivetheir phone through CTI from rich cloud applications, there is a needfor an easy to use and secured way to associate users of this cloudservice with their PBX extension where this service will be enabled.

The prior art provides for a first set of admin-driven solutions. Thesesolutions require involvement of the company administrator, making thesolution costly to manage

One of these solutions consists in leaving the company administratorconfigure, or validate, all associations of end-users with theircorresponding extensions. In this case the end-user is not involved (oronly partially through requesting the service activation to theadministrator) in the association. It requires significant involvementof this administrator, with recurrent actions as news users enroll inthe solution. It also delays availability of the service for end-users,as they have to wait the corporate admin action to benefit the cloudservice. This process might impair adoption of the service in light ofthe efforts required for its activation. Even if the device isconfigured with a first name and a last name on PBX side, so that thecloud service can make a pre-association using the name configured inthe PBX and the name configured in the cloud service, the associationmust still be confirmed by the administrator as it may lead in errorcases and wrong automatic association if the configured names are notexactly the same.

For example, the prior art provides for association methods requiringuser definition in the PBX to be filled with a mail address that has tomatch the cloud account of the user. This procedure requires a deepinvolvement of the administrator as this email address might notpre-exist in the PBX (and of course takes as hypothesis that the PBXdata model includes user email address, further increasing theconditions for the solution to be applicable).

Other solutions are user-driven, as the one proposed in this invention.For example, some social network applications allow easily enrolling amobile device and possibly associate a web account, but such proceduresrely on advanced capabilities available on such mobile devices (Internetconnectivity, camera, necessarily reachable Direct inward dialing(DID)). Such solutions are not applicable with simple PBX devices, andmoreover do not necessarily provide a sufficient level of assurance onthe identities being published (ie the user name might not be fullytrustworthy)

SUMMARY

The invention provides for a method for associating a PBX extension witha user account of a cloud service application for controlling PBXextensions, the cloud service application for controlling PBX extensionsbeing provided by a cloud infrastructure, the cloud infrastructurecomprising at least a cloud service server, the PBX extension belongingto a PBX system, the PBX system further comprising a PBX central unitconnecting PBX extensions to a Public Switched Telephone Network, thePBX central unit and the cloud service server being connected through acomputer telephony integration—CTI—link over an Internet Protocolnetwork, the cloud infrastructure further providing an interactive voiceresponse—IVR—application available to the PBX extensions over the PSTNnetwork, the method comprising: receiving, at the cloud service server,an association request from a user account, the association requestcomprising a PBX extension telephone number, sending, from the cloudservice server, an association code to the user account, sending, fromthe cloud service server to the PBX central unit, a command to monitorthe PBX extension associated to the PBX extension telephone number,sending, from the cloud service server to the PBX central unit, acommand to connect the PBX extension associated to the PBX extensiontelephone number to the IVR application, the command including a publicextension telephone number leading to the IVR application, receiving, atthe cloud service server through the IVR application, an associationcode from the PBX extension, comparing, at the cloud service server, theassociation code received through the IVR application with theassociation code sent to the user account, if the association codereceived from the PBX extension is the same as the association code sentto the user account, associating, at the cloud service server, the PBXextension to the user account, thereby enabling the control of the PBXextension from the user account through the CTI link.

In embodiments, the method further involves detecting, through the IVRapplication, a direct inward dialing number of the calling PBX extensionand associating, at the cloud service server, the detected direct inwarddialing number of the PBX extension with the user account.

The transmission of an activation code to the cloud service user account(the end user) ensures the right person receives the information. Theverification of this code through the CTI connection piloting theassociated PBX extension ensures the operation is done on the right PBXextension and by the right person.

The user-device association method provided by the invention is easy toperform and involves little human interaction, so the operational costsare reduced to the minimum. The method provides guarantees that theassociation is done on the right phone, avoiding configuration mistakesand identity usurpation (fraudulent use of the device), and giving thecloud service provider ways to track and prevent fraudulent actions.

The invention empowers end-users into performing this associationthemselves through an easily applicable method, while providingassurance to the cloud service provider, and to the corporateadministrator, that the operation cannot lead to undetectable invalidassociations.

The user-device association method according to the invention requiresno company neither cloud administrator action, incurring no operationalcost per user for this association action. User enrolment thereforeeasily scales, and such solution shall therefore foster the cloudservice adoption by administrators.

This user-device association method according to the invention does notdisclose company sensitive information such as PBX/Phone passwords tothe cloud service.

This user-device association method according to the invention isapplicable on all PBXs that provide a CTI link.

In embodiments, sending, from the cloud service server to the PBXcentral unit, a command to monitor the PBX extension associated to thePBX extension telephone number, is performed upon receiving anassociation finalization request from the user account.

In embodiments, the method further comprises sending, to the PBX centralunit over the CTI link, a command to lock the PBX extension associatedto the PBX extension telephone number, wherein a local PBX extensioncode is to be dialed at the PBX extension to unlock it, the local PBXextension code being different from the association code.

In embodiments, the method further comprises generating, at the cloudservice server, an association context identifier associated to theassociation code and storing the association code together with theassociation context identifier, wherein the command to connect the PBXextension associated to the PBX extension telephone number to the IVRapplication further includes the association context identifier, andwherein the method further comprises, receiving, at the cloud serviceserver through the IVR application, the association context identifierfrom the PBX central unit, and wherein comparing the association codereceived from the PBX extension with the association code sent to theuser account, includes retrieving the association code sent to the useraccount based on the association context identifier received through theIVR application.

In embodiments, the method further comprises detecting, through the IVRapplication, a direct inward dialing number of the calling PBX extensionand associating, at the cloud service server, the detected direct inwarddialing number of the PBX extension with the user account.

In embodiments, the association code received through the IVRapplication is encoded within a Dual-tone multi-frequencysignaling—DTMF—signal.

The invention also provides a cloud architecture providing a cloudservice application for controlling PBX extensions belonging to a PBXsystem, the PBX system further comprising a PBX central unit connectingPBX extensions to a Public Switched Telephone Network, the cloudinfrastructure comprising at least a cloud service server, the cloudinfrastructure providing an IVR application available to PBX extensionsover the PSTN network, the cloud service server comprising: a CTI linkfor communicating with the PBX central unit over an Internet Protocolnetwork, control means arranged for receiving, at the cloud serviceserver, an association request from a user account, the associationrequest comprising a PBX extension telephone number, sending, from thecloud service server, an association code to the user account, sending,from the cloud service server to the PBX central unit, a command tomonitor the PBX extension associated to the PBX extension telephonenumber, sending, from the cloud service server to the PBX central unit,a command to connect the PBX extension associated to the PBX extensiontelephone number to the IVR application, the command including a publicextension telephone number leading to the IVR application, receiving, atthe cloud service server through the IVR application, an associationcode from the PBX extension, comparing, at the cloud service server, theassociation code received through the IVR application with theassociation code sent to the user account, if the association codereceived from the PBX extension is the same as the association code sentto the user account, associating, at the cloud service server, the PBXextension to the user account, thereby enabling the control of the PBXextension from the user account through the CTI link.

The invention also provides a method for associating a PBX extensionwith a user account of a cloud service application for controlling PBXextensions, the cloud service application for controlling PBX extensionsbeing provided by a cloud infrastructure, the cloud infrastructurecomprising at least a cloud service server, the PBX extension belongingto a PBX system, the PBX system further comprising a PBX central unitconnecting PBX extensions to a Public Switched Telephone Network, thePBX central unit and the cloud service server being connected through aCTI link over an Internet Protocol network, the cloud infrastructurefurther providing an IVR application available to the PBX extensionsover the PSTN network, the method comprising: upon receiving, at the PBXcentral unit, a command from the cloud service server to monitor a PBXextension, the command including a PBX extension telephone number of thePBX extension to monitor, monitoring, at the PBX central unit, the PBXextension associated to the PBX extension telephone number included inthe command, upon receiving, at the PBX central unit, a command from thecloud service server, to connect the PBX extension associated to the PBXextension telephone number with the IVR application, the commandincluding a public extension telephone number leading to the IVRapplication, connecting the PBX extension associated to the PBXextension telephone number with the public extension telephone numberleading to the IVR application, sending, from the PBX extension to thepublic extension telephone number leading to the IVR application, anassociation code dialed at the PBX extension by the user.

In embodiments, the method further comprises: locking the PBX extensionupon receiving, at the PBX extension from the PBX central unit, acommand to lock the PBX extension, unlocking the PBX extension if avalid local PBX extension code is dialed at the PBX extension, the localPBX extension code being different from the association code.

In embodiments, the method further comprises encoding the associationcode dialed at the PBX extension within a Dual-tone multi-frequencysignaling—DTMF—signal.

The invention also provides a PBX system comprising: PBX extensions eachcomprising a user interface arranged for dialing an association code, aPBX central unit comprising control means arranged for connecting thePBX extensions to a Public Switched Telephone Network, a CTI link forcommunicating with a cloud service server over an Internet Protocolnetwork, the cloud service server belonging to a cloud infrastructurefurther providing an IVR application available to the PBX extensionsover the PSTN network, control means arranged for upon receiving acommand from the cloud service server to monitor a PBX extension, thecommand including a PBX extension telephone number of the PBX extensionto monitor, monitoring the PBX extension associated to the PBX extensiontelephone number included in the command, upon receiving a command fromthe cloud service server, to connect the PBX extension associated to thePBX extension telephone number with an IVR application, the commandincluding a public extension telephone number leading to the IVRapplication, connecting the PBX extension associated to the PBXextension telephone number with the public extension telephone numberleading to the IVR application, each PBX extension further comprisingcontrol means arranged for sending, to the public extension telephonenumber leading to the IVR application, an association code dialed at thePBX extension.

The invention also provides a communication system comprising a cloudarchitecture and PBX system.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter, byway of example, with reference to the drawings.

FIG. 1 is a representation of a hybrid system comprising a PBX systemand a cloud architecture.

FIG. 2 illustrates a user-device association method according to theinvention.

FIG. 3 is a message sequence chart of an embodiment of the method ofFIG. 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a representation of a hybrid system comprising a PBX system 20and a cloud architecture 30. The PBX system 20 may in particular belongto a company that has subscribed to the cloud service.

The PBX system 20 comprises a plurality of PBX extensions 21 and atleast a PBX central unit 22. The PBX central units 22 and PBX extensions21 can be on the same site or on different sites. In particular, ifthere is more than one PBX central unit 22, the PBX central units 22 maybe on different sites.

A PBX extension 21 can be any type of phone that is supported by the PBX(IP, TDM, Analog, Softphone), as long as it supports CTI monitoring onthis phone. A PBX extension 21 includes a user interface arranged fordialing an association code. The user interface can be as simple as abasic dial pad.

The PBX system 20 comprises a PBX central unit 22 arranged forconnecting the PBX extensions 21 to a Public Switched Telephone Network40.

A computer telephony integration (CTI) link 51 allows cooperationbetween the PBX system 20 and the cloud infrastructure 30 over anInternet Protocol network 50.

The cloud infrastructure 30 provides a cloud service application forcontrolling PBX extensions belonging to the PBX system 20. The cloudinfrastructure 30 includes at least one cloud service server 32. Thecloud service server 32 may be composed of independent entitiesinteracting together.

The cloud infrastructure 30 further provides an interactive voiceresponse—IVR—application available to the PBX extensions 21 over thePSTN network 40. IVR allows the PBX extensions 21 to interact with usersthrough the use of voice and DTMF tones input via keypad.

A storage space or container (logical or physical), hereafter calledrepository 35, is stored in the cloud architecture 30.

Each end-user of the PBX system 20 has a cloud service user account 31for the cloud service.

The repository 35 registers all the PBX extensions 21 of the PBX system20, and all the service user accounts 31 associated to the PBX system 20in a logical space corresponding to the subscribing company.

A PBX extension 21 can only be associated to a cloud service useraccount 31 if the cloud service user account 31 and PBX extension 21 areregistered in the same repository 35.

The PBX extensions 21 or set of PBX extensions 21 of the PBX system 20are connected to the cloud architecture 30 through a CTI link 51providing a CTI connectivity between the cloud service and the PBXcentral unit 22, allowing CTI-driven actions from the cloud applicationsto the PBX extension, during and after their association to an end-user.

The method for associating a PBX extension 21 with a user account 31 ofa cloud service application for controlling PBX extensions comprises thefollowing steps.

Logged into his user account 31 of the cloud service application, usingfor example a desktop, or a mobile phone, the end user can start a PBXextension association by entering, in the cloud service application, hisPBX extension telephone number as it is known at the PBX level (ie thisis the internal phone number of the end-user in the corporate PBXsystem). This step can either be done by the user manually entering aPBX extension telephone number (the cloud service then verifies that theextension telephone number is registered in the repository 35 associatedto the PBX system of the user, or by picking up a choice among arestricted list of extension telephone number that the cloud service maybuild by comparing the name of the user as known at the cloud accountlevel, with information retrieved from the PBX database (typical phonebook information retrieved from the PBX and mapping extension topeople's names).

Upon receiving, at a step S1, the association request comprising theuser account 31 identifier and the PBX extension telephone numberentered by the end user, the cloud service server 32 generates, storesin its memory, and sends, at a step S2, an association code to the userof the user account that generated the association request. Theassociation code may for example be a simple Personal identificationnumber (PIN) code made of a 4 digits. The association code may inparticular be sent to the cloud service user account 31 through thecloud service application. It may also be sent through an out-of-bandmethod. Using an out-of-band method reduces the risk of someone havingstolen the credentials of the cloud service account doing the operation,and also allows the cloud service operator more easily logging andauditing the operation. The out-of-band method can for example be peremail or mobile phone, at the condition that the information (email ormobile phone respectively) was created and verified at cloud serviceaccount creation and cannot be modified afterwards without cloudprovider verification.

At a step S21, the cloud service server 32 may generate an associationcontext identifier. The association context identifier is storedtogether with the association code generated at step S2.

Once the user receives the association code, he may have to requestassociation finalization from his cloud service application user account31, by sending at an optional step S3 a finalization request to thecloud service server 32. The next steps require that the user bephysically present near the associated phone. The finalization requestindicates that the user is near the phone and that the process maycontinue.

Upon receiving, at step S1, the association request, (or if a request ofassociation finalization is required, upon receiving, at step S3, arequest of association finalization), the cloud service server 32automatically starts monitoring the extension 21 that is beingassociated, thanks to the CTI link 51 that is established between thecloud service server 32 and the PBX central unit 22. To that end, thecloud service server 32 sends, at a step S4, a command to the PBXcentral unit 22 to monitor the PBX extension 21 associated to the PBXextension telephone number. Upon receiving the command from the cloudservice server 32, at a step S11, the PBX central unit 22 startsmonitoring, the PBX extension 21 associated to the PBX extensiontelephone number included in the command.

The cloud service server 32 may optionally send, at a step S5, a CTIcommand to the PBX central unit 21 to lock the monitored extension 21that forces the extension 21 to get locked, resulting in the requirementfor a local PBX extension code to be manually entered by the user beforeany new external call can take place, explicitly confirming that theuser owns the extension 21. The way the CTI command actually results inthe extension 21 getting locked, at a step S22, depends on the phone andPBX implementation. It can for example consist in a third party callcontrol (SPCC) call made between the extension 21 and a specific prefixthat is interpreted by the PBX central unit 22, that then forces theextension 21 to lock itself, or could alternatively be translated by thePBX central unit 22 to directly send a notification to the extension 21,at a step S13, so it locks itself.

Step S5 is optional as it is only applicable to environments thattechnically support it (phones must support being locked to preventother people than the device owner to use it, and the feature has to beavailable thru CTI PBX), and where the practice of using the local codehas been deployed, so users know what their device local code is. Thecloud service allows the company administrator to activate this securitystep for user/device associations when all these pre-requisites are met.

If this step is not enforced, the proximity of the user with the phonehas to be considered a good-enough indication that the person is thelegitimate one (knowing that step S2 allows tracking who received theassociation code, and pre-requisites ensure only users of the companycan associate a phone of this company).

The local code is purely local to the enterprise telephony installationand specific to the phone or phone user (phones may be shared in desksharing environment, in which case the phone code is rather specific toa user). This code may be chosen by the phone user, and can be comparedto a mobile phone PIN code. It is not known to the cloud service, and istotally different from the association code sent in step S2.

The cloud service server 32 sends, at a step S6, a command to the PBXcentral unit 22 to connect the PBX extension 21 associated to the PBXextension telephone number to the IVR application 33, the commandincluding a public extension telephone number leading to the IVRapplication 33 managed by the Cloud Service provider. This can be doneby triggering a CTI MakeCall on the associated extension.

Upon receiving, at a step S14, the command from the cloud service server32, the PBX central unit 22 connects the PBX extension 21 associated tothe PBX extension telephone number with the public extension telephonenumber leading to the IVR application 33.

To that end, the PBX central unit 22 calls, at a step S15, the PBXextension 21 associated to the PBX extension telephone number, and, at astep S16, the public extension telephone number leading to the IVRapplication 33.

The command to connect the PBX extension 21 to the IVR application 33may further includes the association context identifier set at step S21.

The association context identifier may for example be sent to the IVRapplication in the form of a set of DTMF digits in the MakeCall inaddition to the IVR public extension (for example MakeCall dials0033390677069*1234567 #).

The association context identifier may alternatively be sent throughDTMF over the established connection.

Upon reception, the context identifier digits are automatically dialed,at step S16, by the PBX central unit 22 to the IVR application 33. Thecontext identifier can be used by the IVR application to retrieve thecontext of the association being confirmed. This method allows the cloudservice server 32 unambiguously identifying the incoming call, even ifthe association code generated at step S2 is not unique. It could bedone differently, for example by imposing long association code to endusers, ensuring their uniqueness in the timeframe of possibly parallelassociations if the cloud service must serve a high rate of usersenrolment, or by using a large set of IVR extensions and distributingparallel enrolments over the different public numbers.

If the phone was locked in step S22, before the CTI call can actually beplaced by the extension 21, the extension 21 prompts, at a step S24, theuser to enter his local code. The user enters the local code and thephone validates and unlocks, at a step S25. If the code entered isinvalid, the call fails and the association procedure is stopped. It canpossibly be retried by looping on Step S3.

The call from the PBX central unit 21 reaches the IVR application of theCloud Service at a step S31. The IVR application prompts, at a step S33,the user to provide the association code through DTMF or other methodallowing recognizing digits. This is typically done by vocalinstructions or by displaying a message on the PBX extension interface.

The user enters the association code through the interface of his PBXextension 21. The PBX extension 21sends, at a step S27, the associationcode dialed by the user on the connection established with the IVR. Theassociation code is typically encoded within a DTMF signal.

Upon reception of the call from the PBX extension 21, the IVRapplication 33 may detect a direct inward dialing number of the callingPBX extension 21. This number will be associated with the user accountat a later step S10.

The cloud service server 32 receives, through the IVR application 33,the association code at a step S8.

The received association code, possibly correlated to the associationcontext identifier received at step S31, allows the cloud service server32 to finalize the association.

The cloud service server 32 compares, at a step S9, the association codereceived from the PBX extension 21 with the association code sent to theuser at step S2.

If an association context identifier was received through the IVRapplication 33 at step S31, the cloud service server first retrievesfrom his memory the association code sent to the user at step S2 basedon the context identifier.

If the association code entered by the end-user on the phone correspondsto the expected code (as sent in step S2 and retrieved by the cloudservice), the association is confirmed, at a step S10, and the cloudservice definitely enables CTI services on this extension from the useraccount. If a direct inward dialing number of the calling PBX extension21 was detected by the IVR application at step S32, the detected directinward dialing number of the PBX extension 21 is associated with theuser account.

At a step S36, the cloud service server 32 may send a successfulassociation notification to the user account though the IVR application.

Elements such as the cloud service server 32, PBX extensions 21 and PBXcentral unit 22 could each be e.g. hardware means like e.g. anapplication-specific integrated circuit (ASIC), or a combination ofhardware and software means, e.g. an ASIC and an field-programmable gatearray (FPGA), or at least one microprocessor and at least one memorywith software modules located therein.

The invention is not limited to the described embodiments. The appendedclaims are to be construed as embodying all modifications andalternative constructions that may occur to one skilled in the art, andwhich fairly fall within the basic teaching as set forth herein.

The use of the verb “to comprise”, “to include” or “to contain” andtheir conjugations does not exclude the presence of elements or stepsother than those stated in a claim. Furthermore, the use of the article“a” or “an” preceding an element or step does not exclude the presenceof a plurality of such elements or steps.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the scope of the claims.

The invention claimed is:
 1. A method for associating a PBX extensionwith a user account of a cloud service application for controlling PBXextensions, the cloud service application for controlling PBX extensionsbeing provided by a cloud infrastructure, the cloud infrastructurecomprising at least a cloud service server, the PBX extension belongingto a PBX system, the PBX system further comprising a PBX central unitconnecting PBX extensions to a Public Switched Telephone Network (PSTN),the PBX central unit and the cloud service server being connectedthrough a computer telephony integration (CTI) link over an InternetProtocol network, the cloud infrastructure further providing aninteractive voice response (IVR) application available to the PBXextensions over the PSTN network, the method comprising: receiving, atthe cloud service server, an association request from a user account,the association request comprising a PBX extension telephone number,sending, from the cloud service server, an association code to the useraccount, sending, from the cloud service server to the PBX central unit,a command to monitor the PBX extension associated to the PBX extensiontelephone number, sending, from the cloud service server to the PBXcentral unit, a command to connect the PBX extension associated to thePBX extension telephone number to the IVR application, the commandincluding a public extension telephone number leading to the IVRapplication, receiving, at the cloud service server through the IVRapplication, an association code from the PBX extension, comparing, atthe cloud service server, the association code received through the IVRapplication with the association code sent to the user account, if theassociation code received from the PBX extension is the same as theassociation code sent to the user account, associating, at the cloudservice server, the PBX extension to the user account, thereby enablingthe control of the PBX extension from the user account through the CTIlink.
 2. The method according to claim 1, wherein sending, from thecloud service server to the PBX central unit, a command to monitor thePBX extension associated to the PBX extension telephone number, isperformed upon receiving an association finalization request from theuser account.
 3. The method according to claim 2, further comprisingdetecting, through the IVR application, a direct inward dialing numberof the PBX extension and associating, at the cloud service server, thedetected direct inward dialing number of the PBX extension with the useraccount.
 4. The method according to claim 2, further comprising:sending, to the PBX central unit over the CTI link, a command to lockthe PBX extension associated to the PBX extension telephone number,wherein a local PBX extension code is to be dialed at the PBX extensionto unlock it, the local PBX extension code being different from theassociation code.
 5. The method according to claim 2, further comprisinggenerating, at the cloud service server, an association contextidentifier associated to the association code and storing theassociation code together with the association context identifier,wherein the command to connect the PBX extension associated to the PBXextension telephone number to the IVR application further includes theassociation context identifier, wherein the method further comprises,receiving, at the cloud service server through the IVR application, theassociation context identifier from the PBX central unit, and whereincomparing the association code received from the PBX extension with theassociation code sent to the user account, includes retrieving theassociation code sent to the user account based on the associationcontext identifier received through the IVR application.
 6. The methodaccording to claim 1, further comprising: sending, to the PBX centralunit over the CTI link, a command to lock the PBX extension associatedto the PBX extension telephone number, wherein a local PBX extensioncode is to be dialed at the PBX extension to unlock it, the local PBXextension code being different from the association code.
 7. The methodaccording to claim 6, further comprising generating, at the cloudservice server, an association context identifier associated to theassociation code and storing the association code together with theassociation context identifier, wherein the command to connect the PBXextension associated to the PBX extension telephone number to the IVRapplication further includes the association context identifier, andwherein the method further comprises, receiving, at the cloud serviceserver through the IVR application, the association context identifierfrom the PBX central unit, and wherein comparing the association codereceived from the PBX extension with the association code sent to theuser account, includes retrieving the association code sent to the useraccount based on the association context identifier received through theIVR application.
 8. The method according to claim 7, further comprisingdetecting, through the IVR application, a direct inward dialing numberof the PBX extension and associating, at the cloud service server, thedetected direct inward dialing number of the PBX extension with the useraccount.
 9. The method according to claim 6, further comprisingdetecting, through the IVR application, a direct inward dialing numberof the PBX extension and associating, at the cloud service server, thedetected direct inward dialing number of the PBX extension with the useraccount.
 10. The method according to claim 1, further comprisinggenerating, at the cloud service server, an association contextidentifier associated to the association code and storing theassociation code together with the association context identifier,wherein the command to connect the PBX extension associated to the PBXextension telephone number to the IVR application further includes theassociation context identifier, and wherein the method furthercomprises, receiving, at the cloud service server through the IVRapplication, the association context identifier from the PBX centralunit, and wherein comparing the association code received from the PBXextension with the association code sent to the user account, includesretrieving the association code sent to the user account based on theassociation context identifier received through the IVR application. 11.The method according to claim 10, further comprising detecting, throughthe IVR application, a direct inward dialing number of the PBX extensionand associating, at the cloud service server, the detected direct inwarddialing number of the PBX extension with the user account.
 12. Themethod according to claim 1, further comprising: locking the PBXextension upon receiving, at the PBX extension from the PBX centralunit, a command to lock the PBX extension, unlocking the PBX extensionif a valid local PBX extension code is dialed at the PBX extension, thevalid local PBX extension code being different from the associationcode.
 13. The method according to claim 12, further comprising encodingthe association code dialed at the PBX extension within a Dual-tonemulti-frequency signaling (DTMF) signal.
 14. The method according toclaim 1, further comprising encoding the association code dialed at thePBX extension within a Dual-tone multi-frequency signaling—DTMF—signal.15. A cloud infrastructure providing a cloud service application forcontrolling PBX extensions belonging to a PBX system, the PBX systemfurther comprising a PBX central unit connecting PBX extensions to aPublic Switched Telephone Network (PSTN), the cloud infrastructurecomprising at least a cloud service server, the cloud infrastructureproviding an IVR application available to PBX extensions over the PSTNnetwork, the cloud service server comprising: a CTI link forcommunicating with the PBX central unit over an Internet Protocolnetwork, control means arranged for receiving, at the cloud serviceserver, an association request from a user account, the associationrequest comprising a PBX extension telephone number, sending, from thecloud service server, an association code to the user account, sending,from the cloud service server to the PBX central unit, a command tomonitor the PBX extension associated to the PBX extension telephonenumber, sending, from the cloud service server to the PBX central unit,a command to connect the PBX extension associated to the PBX extensiontelephone number to the IVR application, the command including a publicextension telephone number leading to the IVR application, receiving, atthe cloud service server through the IVR application, an associationcode from the PBX extension, comparing, at the cloud service server, theassociation code received through the IVR application with theassociation code sent to the user account, if the association codereceived from the PBX extension is the same as the association code sentto the user account, associating, at the cloud service server, the PBXextension to the user account, thereby enabling the control of the PBXextension from the user account through the CTI link.
 16. The cloudinfrastructure according to claim 15, wherein: the PBX extensions eachcomprise a user interface arranged for dialing an association code, andthe PBX central unit comprises control means arranged for: uponreceiving a command from the cloud service server to monitor a PBXextension, the command including a PBX extension telephone number of thePBX extension to monitor, monitoring the PBX extension associated to thePBX extension telephone number included in the command, upon receiving acommand from the cloud service server, to connect the PBX extensionassociated to the PBX extension telephone number with an IVRapplication, the command including a public extension telephone numberleading to the IVR application, connecting the PBX extension associatedto the PBX extension telephone number with the public extensiontelephone number leading to the IVR application, each PBX extensionfurther comprising control means arranged for sending, to the publicextension telephone number leading to the IVR application, anassociation code dialed at the PBX extension.